A vane pump includes a rotor in which vanes are received, a cam ring that has an inner circumferential cam face with which tip portions of the vanes slidingly contact, and a side plate that slidingly contact with one end side of the rotor in the axial direction. The side plate is provided with a suction port and a discharge port, each of the suction port and the discharge port is formed in an arc shapes, the suction port guides working fluid into pump chambers defined by the rotor, the cam ring, and the adjacent vanes, and a discharge port guides the working fluid discharged from the pump chambers.
Furthermore, the side plate is provided with a back pressure port that guides the working fluid, which is discharged from the discharge port, to back-pressure chambers defined on the base-end sides of the vanes. With such a configuration, because the vanes are pressed radially outward by the pressure of the working fluid in the back-pressure chambers, tip ends of the vanes can slidingly contact with the inner circumference of the cam ring over the whole circumference of the rotor.
JP2003-97453A discloses a technique where each of a back pressure port at suction side and a back pressure port at discharge side is formed in an arc shape, both ends of the back pressure ports are communicated through orifice grooves, the back pressure port at the suction side is provided for introducing, to back-pressure chambers, working fluid discharged from a discharge port in a suction section in which the working fluid is guided to pump chambers, and the back pressure port at the discharge side is provided for introducing, to the back-pressure chambers, the working fluid discharged from the discharge port in a discharge section in which the working fluid is discharged from the pump chambers.